A microgrid is a localized grouping of electricity generation, energy storage, and loads that normally operates connected to a traditional centralized grid (power distribution grid or macrogrid) via a point of common coupling (PCC). This single point of common coupling with the macrogrid can be disconnected, islanding the microgrid. Microgrids are part of a structure aiming at producing electrical power locally from many small energy sources, Distributed Generators (DGs). In a microgrid, a DG is connected via a converter or synchronous machine which controls the output of the DG, i.e. the current injected into the microgrid.
A microgrid (in grid connected mode, i.e. connected to the macrogrid) supplies the optimized or maximum power outputs from the connected DG sites and the rest of the power is supplied by the macrogrid. The microgrid is connected to the macrogrid at a PCC through a controllable switch. This grid connection is lost during grid fault and the microgrid is islanded.
A microgrid is controlled by a controller, which may be centralized or distributed, which e.g. controls DGs in accordance with voltage or current control schemes. One of the aspects of microgrid control is efficient control of the grid interface at the PCC. Various conditions e.g. power flow, voltage, disconnection or power factor at the PCC impose different control requirement within the microgrid.
There are various methods to control the grid interface and one of them is to have a dedicated network controller. The network controller can monitor and communicate different system conditions to other controllers within the microgrid (e.g. status of the grid circuit breaker). The network controller can participate in various functions such as black start, resynchronization, planned islanding, voltage droop for the microgrid as well as power factor correction.
CN 104467010 discloses a microgrid divided into a plurality of sub-microgrids, each having a microgrid controller communicating with a main microgrid controller.